Signal Transducer and Activator of Transcription (STAT) proteins are transcription factors that mediate cellular responses to growth factors. These proteins are activated via tyrosine phosphorylation by growth factor receptor-associated tyrosine kinases. Activated STAT proteins promote cell survival and proliferation. It is now well established that persistent activation of STAT3 or STAT5 promotes cell growth, invasion, and metastasis of both solid and hematopoietic cancers. See, e.g., Expert Opin. Investig. Drugs, 2009, 18(1): 45-56.
In normal lymphoid cells, STAT proteins, e.g., STAT3, also mediate cellular responses to cytokines, such as interleukin-6 (IL-6), via cytokine receptor-associated Janus kinases (JAKs). See, e.g., Neoplasia 2008, 10: 287-297. IL-6 is abnormally elevated in patients suffering from hematopoietic cancers, inflammatory diseases, autoimmune diseases, and postmenopausal osteoporosis. Inhibiting cellular action of IL-6, e.g., by inducing STAT3 proteins degradation, has attributed to treatment of these diseases.
As such, compounds that deactivate STAT proteins can be used to treat various cancers, inflammatory diseases, and autoimmune diseases.